On Sat, 1 Feb 2014, Brown, Len wrote: > > Right now (on ARM at least but I imagine this is pretty universal), the > > biggest impact on information accuracy for a CPU depends on what the > > other CPUs are doing. The most obvious example is cluster power down. > > For a cluster to be powered down, all the CPUs sharing this cluster must > > also be powered down. And all those CPUs must have agreed to a possible > > cluster power down in advance as well. But it is not because an idle > > CPU has agreed to the extra latency imposed by a cluster power down that > > the cluster has actually powered down since another CPU in that cluster > > might still be running, in which case the recorded latency information > > for that idle CPU would be higher than it would be in practice at that > > moment. > > That will not work.
What will not work? > When a CPU goes idle, it uses the CURRENT criteria for entering that state. > If the criteria change after it has entered the state, are you going > to wake it up so it can re-evaluate? No. That's not what I'm saying at all. > That is why the state must describe the worst case latency > that CPU may see when waking from the state on THAT entry. No disagreement there. Isn't that what I'm saying? > That is why we use the package C-state numbers to describe > core C-states on IA. And your point is? Nicolas -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
